Nd含量对磁控溅射Si(111)/Cr/Nd-Co/Cr薄膜结构与磁性的影响

Effect of Nd Content on the Structure and Magnetic Properties of Si(111)/Cr/Nd-Co/Cr Thin Films Prepared by Magnetron Sputtering

采用磁控溅射技术制备了系列Si(111)/Cr(10 nm)/NdCox(400 nm)/Cr(10 nm)薄膜,其中,Co/Nd原子比x=2.5~7.2。利用XRD、SEM、AFM/MFM、VSM等手段研究了Nd含量对制备态薄膜垂直磁各向异性(PMA)与磁畴结构及退火态薄膜相结构与磁性的影响规律。结果表明,随着Nd含量的变化,制备态Nd-Co薄膜的垂直磁各向异性能Ku在x=5.2附近存在一个较宽的峰,峰值处Ku=(80±5) kJ/m3。MFM图像的相移均方根偏差(Δφrms)在临界成分χ=5.2处也存在最大值,其成分依赖关系与Ku-x的变化趋势一致。薄膜应力诱导的磁弹各向异性是导致溅射Nd-Co非晶薄膜PMA的主要原因。经过在600℃真空快速退火后,所有薄膜均析出了Nd2Co17、NdCo2、Nd4Co3等金属间化合物,而NdCo5±x相纳米晶只在Nd过量(至少4%,原子分数)的χ=2.5和3.8薄膜中才被观测到,同时还伴随着Nd2Co7共生相的析出。室温磁性测试结果表明,NdCo5±x和Nd2Co7相纳米晶的析出,导致χ=2.5和3.8薄膜面内矫顽力(分别为Hc-in=54和51 kA/m)显著增强;而x≥4.4样品的面内矫顽力保持在低值(Hc-in=4~8 kA/m)范围内。

A series of Si(111)/Cr(10 nm)/NdCox(400 nm)/Cr(10 nm) thin films with the atomic ratio of Co/Nd(x) varying from 2.5 to 7.2 were prepared by radio frequency magnetron sputtering. The influence of Nd content on the structure and magnetic properties of the as-prepared and post annealed films were investigated by XRD, SEM, VSM and AFM/MFM. Magnetic measurements at room temperature show that the compositional variation of the perpendicular anisotropy energy(Ku) exhibits a broad peak around χ=5.2 with maximum of Ku=(80±5) kJ/m3 for the as-prepared Nd-Co amorphous films. MFM characterization shows that the root mean square deviation of phase shift in MFM images(Δφrms) also have a compositional dependence which is similar to that of Ku-x. The experimental results show that the stress induced magneto-elastic anisotropy is the primary origin of the perpendicular magnetic anisotropy(PMA) in the asprepared Nd-Co amorphous film. After rapid thermal annealing(RTA) process in a vacuum atmosphere at600 °C, intermetallic compounds such as Nd2 Co17, Nd4Co3 and NdCo2 are precipitated in all the studdied films, while NdCo5±xnanocrystals accompanied by the precipitation of Nd2Co7 symbiotic phase were observed only in the films with χ=2.5 and 3.8(the atomic fraction of Nd excesses at least 4%). The in-plane coercivity of the films with χ=2.5 and 3.8 was significantly enhanced(Hc-in=54, 51 kA/m) due to the precipitation of NdCo5±xand Nd2Co7 nanocrystals, while that of the samples with x>4.4 remained low value(Hc-in=4~8 kA/m).